This invention relates to an apparatus for supplying a polishing solution for use in polishing, for example, a semiconductor substrate, and relates in particular to an apparatus for steadily supplying a polishing solution having a constant dispersion of abrading particles in the liquid.
Recent advances in circuit integration in semiconductor devices have produced micro-sized circuit patterns with narrow line widths. As a result, circuit pattern printing by optical lithography requires extremely shallow depth of focus, so that the substrate surface needs to be precisely flat in the focal plane of the stepper apparatus.
A method of obtaining a flat surface on a semiconductor substrate is to polish the wafer using a polishing tool (for example, polishing table with a polishing cloth), and a wafer holding member for holding and pressing the surface to be polished of the wafer against the polishing table, and moving the surface to be polished relative to the polishing tool while supplying a polishing solution at the contact interface between the polishing tool and the surface to be polished. Such a polishing apparatus can perform not only mechanical polishing using a polishing solution containing abrasive particles, but can also perform chemical polishing using an alkaline or acidic polishing solution. For example, a slurry for polishing an oxidized surface of the wafer is based on a KOH or NH4OH solution with a dispersion of silica particles.
To produce a good substrate using such a polishing apparatus, it is required that the polishing solution of a constant concentration be steadily supplied at a constant rate. A system for supplying a polishing solution has an undiluted solution tank to store a mixed solution of KOH, NH4OH and silica powder; a dilution tank to dilute the undiluted solution with pure water and others; and a supply piping to deliver the solution from the dilution tank to the nozzle of the polishing apparatus.
However, to meet the demand of cost reduction for equipment and operation, it is desired to supply the polishing solution from one tank to a plurality of polishing apparatuses, so that there is a tendency for long lengths of delivery piping. As a result, the polishing solution becomes stagnant inside the piping and tends to cause aggregation of abrasive particles so that the abrasive particles tend to cluster, thereby causing damage (scratch) to the substrate surface, thereby changing the amount of polishing as a result of changes in solution concentration, or thereby plugging the piping.
This invention is presented in view of the problems outlined above, and it is an object of the present invention to provide a polishing apparatus that can supply a polishing solution, having a non-varying distribution of abrading particle sizes, at a steady rate.
The invention includes an apparatus for delivering a polishing solution to a polishing apparatus, with the apparatus comprising: a solution passage for transporting the polishing solution; and an ultrasonic vibrator being provided in at least one location of the solution passage. Accordingly, clustered powder particles are dispersed by the ultrasonic vibration, so that a polishing solution, having a constant size distribution of fine powder particles in a given size range, can be delivered to the polishing apparatus. The dispersion effect of the treatment is retained for some time after applying the ultrasonic vibration, so that the particles are prevented from clustering while the solution is being delivered through the solution passage to reach the polishing apparatus.
The ultrasonic vibrator can be provided in a stock tank for storing an undiluted solution. The stock tank may be a storage tank for storing an undiluted solution delivered from an external source, or a tank to prepare a polishing solution by mixing powder particles and a solution to produce an undiluted solution or a polishing solution.
The solution passage may have a circulation passage for circulating the polishing solution and a delivery passage extending from the circulation passage to a polishing apparatus, and the ultrasonic vibrator can be provided on the circulation passage. Accordingly, non-stopping circulation of the polishing solution inside the solution passage prevents changes in the concentration of the solution or plugging in the passage caused by precipitated solid clusters of powder particles inside the passage. Also, one solution supply apparatus can deliver a polishing solution from one supply source to a number of polishing apparatuses, so that the apparatus cost can be lowered.
The ultrasonic vibrator can also be provided on the delivery passage. Also, the polishing solution may contain powder particles in a range of particle sizes between 0.1 to 0.2 xcexcm.
The ultrasonic vibrator can be provided in a mixing section for mixing an undiluted solution and a dilution solution for adjusting a solution concentration.
The invention also includes a polishing apparatus which comprises a holding device for holding an object to be polished, a polishing tool opposing the holding device and a spray nozzle for introducing a polishing solution at an interface between the object to be polished and the polishing tool, wherein an ultrasonic vibrator is provided on those parts of the holding device and/or the polishing tool that retain the polishing solution.